Bitumen blasting process and apparatus therefor

ABSTRACT

Soft asphalt is hardened by passing a stream of air into and through the asphalt in a molten state. The air stream forms air bubbles which rise through the asphalt. The air bubbles are forcibly coalesced into air sacs and the air sacs are redispersed into air bubbles. The air bubbles may be coalesced into air sacs and redispersed more than once.

United States Patent Senolt et al.

BITUMEN BLASTING PROCESS AND APPARATUS THEREFOR Inventors: Hans Senolt;Heinrich Tomaschko; Georg Palvik, all of Vienna, Austria OsterrelchischeMineralolverwaltung Aktiengesellschaft, Vienna, Austria Filed: July 23,1969 Appl. No.: 843,955

Assignee:

Foreign Application Priority Data July 25, 1968 Austria ..A 7211/68 u.s.Cl ..208/6 Int. Cl ...Cl0g 1/00 Field 01 Search ..208/6 n51 us [451 air.2, 1972 [56] Reierences Cited UNITED STATES PATENTS 1,901,172 3/1933Kirk ....208/6 1,306,520 6/1919 Burk1ey.. ....208/6 1,259,674 3/1918Roseu..... ....208/6 2,170,496 8/1939 Gard ..208/6 PrimaryExaminer-Delbert E. Gantz Assistant Examiner-Veronica OKeefeAttorney-Holman & Stern [57] ABSTRACT Soft asphalt is hardened bypassing a stream of air into and through the asphalt in a molten state.The air stream forms air bubbles which rise through the asphalt. The airbubbles are forcibly coalesced into air sacs and the air sacs areredispersed into air bubbles. The air bubbles may be coalesced into airsacs and redisperscd more than once.

2 Claims, 1 Drawing Figure PATENTEnmzs m2 -20 j I -16 I INVENTQRS HANSSENQLT HEINRICH TOMASCHKO GEORG PALVIK l9 Wanda-vs BITUMEN BLASTINGPROCESS AND APPARATUS THEREFOR The invention relates to an asphaltblowing process. Asphalt is a very viscous liquid, consistingessentially of hydrocarbons and is soluble in carbon disulphide. It issubstantially nonvolatile and softens gradually when heated. It is blackor brown in color and possesses waterproofing and adhesive properties.It is obtained principally by refinery processes from petroleum oil, andis also found as a natural deposit or, in association with mineralmatter as a component of naturally occurring asphalt.

Asphalt is a natural or artificial mixture of bitumen with a substantialportion of solid mineral matter.

The known asphalt blowing process is used to produce mineral oilasphalts of a desired consistency, i.e. of a particular hardness, frommineral oil distillation residues or so-called soft asphalt. The softasphalt is heated to a temperature of 250 C. and thus made highly liquidin a blowing vessel (a vertical cylindrical vessel) and is brought intointimate contact with fresh air blown into the asphalt in the base ofthe blowing vessel and the air is finely dispersed. As the air bubblesrise in the blowing vessel contents part of the oxygen contained in eachbubble penetrates into the surrounding soft asphalt and there formsoxygen addition products in the form of peroxides and/or hydroperoxides.The air bubbles burst on reaching the surface of the reaction materialand the gas contained, that is the waste air impoverished of oxygen,flows through the blowing vessel head to a waste air line. The oxygenaddition products formed by contact of the soft asphalt with the airbubbles are dispersed in the asphalt and there react again to formproducts of the desired consistency. This process is carried out untilthe asphalt has reached the desired degree of consistency.

The economics of the blowing process depend essentially on two factors,namely the time required to produce a given end product from a giveninitial product, that is consistency increase per unit time, and on theconsumption of finely dispersed fresh air, that is the number of cubicof air required per ton and consistency increase. The former factordetermines the amount of investment in plant and the operational timecost per ton of finished product, and the second factor the cost ofinvestment in the operation medium, that is the blowing air, togetherwith the required energy consumption. All efforts to improve theeconomic efficiency of the blowing process therefore have to be directedtowards shortening the blowing times as much as possible and consumingthe blowing air as extensively as possible.

As has already been indicated, the blowing process proceeds essentiallyin two stages. In the first stage the oxygen contained in the bubblesdiffuses into the soft asphalt surrounding the bubbles, that is it isbrought to a reactant contained in the soft asphalt. In the second stagethe chemical reaction between the introduced oxygen and the reactanttakes place. It has been shown that the first stage, that is thediffusion of the oxygen, as the slower stage of the asphalt blowingprocess is the one which determines the time taken for the process. Itis expressed by the Pick equation W k-A-P-t/s where W is the volume ofdiffusing gas, k the difi'usion rate constant, A the diffusion area, Pthe driving oxygen partial pressure, 1 the diffusion time and s thedensity of the respective film to be penetrated. If W is to beincreased, then the factors k, A, P, t must be increased or s decreased.

The diffusion rate constant k as a material constant depends only on theviscosity, that is on the temperature of the asphalt. Since this for thesake of the reaction must not exceed a certain value (about 250 C.),increasing the diffusion by raising this constant cannot be envisaged.The latter, by contrast, becomes smaller and smaller during the processsince the aim of the blowing process is in fact to achieve a specificincrease in the consistency of the asphalt.

The diffusion area A can be increased in two ways, namely by increasingthe number of air bubbles injected into the blowing vessel risingthrough its contents, and by decreasing the size of the bubbles. Withrespect to increasing the number of bubbles, there are relatively narrowlimits on this since if there is a small mutual separation between thebubbles the bubbles will join together to form larger bubbles. Toprevent the formation of larger bubbles and the associated decrease inthe diffusion area, at the points in the blowing vessel at whichcoalescence of the bubbles is to be expected means are provided tocounteract coalescence of the bubbles or to reverse previous coalescenceby redispersal. The number of bubbles and therefor the dimensions of thediffusion area remain limited in every case. On the other hand, withrespect to reducing the size of the air bubbles, l,000 air bubbles forexample with a radius of 0.5 mm. contain the same amount of air as onebubble with a radius of 5 mm., but have times the surface area. But theenergy required to create bubbles with 1 mm. diameter is 9 times thatfor bubbles with a diameter of IO It also proves problematic to increasethe diffusion by increasing the oxygen partial pressure P. Blowing underincreased pressure does raise the oxygen partial pressure in the airbubbles, but also increases by the same amount the oxygen partialpressure in the exhaust system and hence the danger of secondaryreactions and explosions in the waste air. The same is true forincreasing the partial pressure by adding oxygen (0 or ozone (O andchlorine (C1 or nitrogen dioxide (N0 or to the blast air, chlorine andnitrogen dioxide also having the disadvantage that they producetechnically unsuitable by-products, in the waste air. it also has to beremembered that an air bubble is a completely closed system, due towhich the initial partial pressure in the bubble drops very rapidly asthe oxygen on the one hand is consumed by the asphalt, on the other handis diluted by back diffusion of reaction products such as water andcarbon dioxide (CO in addition to which the bubbles are subject to aconstantly decreasing static liquid pressure as they rise in theasphalt.

With respect to the diffusion time t, it is a known practice to increasethis by increasing the height of the reactor, but this means added costsof construction.

The principle aim of the invention is to increase the economicefliciency of the blowing process. The invention arises fromconsiderations relating to the last parameter appearing in Ficksformula, that is the respective film thickness to be penetrated. Toincrease the diffusion, this has to be kept as small as possible. At theinstant when the bubbles are formed, air and fresh asphalt are in directcontact in every case. But when the reacting components in the boundarysurfaces have been consumed, the oxygen has to penetrate deeper into theasphalt film to meet its reactant. The resistance to difiusion thusincreases, the driving oxygen partial pressure at the same time beingreduced for the reasons already given (oxygen absorption by the asphalt,additional decrease in oxygen content due to back diffusion of reactionproducts, reduction in the static liquid pressure as the bubbles rise).As a result the difiusion process rapidly comes to a halt.Investigations into this have shown that the oxygen diffusion into theasphalt which essentially determines the economic efficiency of theblasting process and the quality of the end product, in fact ceases whenthe air bubbles have only travelled a fraction of their path from thepoint at which they are produced, that is the device by which fresh airis injected into the lower part of the blowing vessel, up to the surfaceof the asphalt, and when only about a third of the oxygen in the bubbleshas been consumed.

Accordingly the invention provides an asphalt blowing process comprisingpassing an air stream through molten asphalt, wherein air bubbles areformed in the asphalt, the air bubbles are forcibly coalesced, and theresultant air sacs are redispersed, thereby creating new air/asphaltphase boundary surfaces. Whereas up to no coalescence of the individualbubbles was prevented by all possible means, according to the presentinvention exactly the opposite is brought about, namely extensivecombination of the bubbles to form large air sacs. This gives rise toextensive breaking up of the liquid phase boundary surfaces of the gasesforming the bubbles, which have already taken part in the reaction andprevent further oxygen diffusion, since the surface area of the air sacsformed by forced coalescence of bubbles will always be smaller than thesum of the surface areas of the bubbles. At the same time the gaseousphases formed by the bubbles are forcibly stripped from the surroundingfilms which have already reacted, and escape into the reaction material.If the forcibly formed air sacs are then redispersed into bubbles, thesewill be surrounded by as yet unconsumed, therefore again reactive,liquid boundary surfaces so that difiusion of the oxygen into theasphalt begins again at a higher rate. As will be seen from the examplesgiven below, in this way the asphalt blowing process is considerablyaccelerated accompanied by a significant saving in the blowing air.

The forced coalescence and redispersion of the air can be repeated anumber of times, advantageously as often as oxygen is still found to bepresent in the bubbles.

The invention also provides an asphalt reactor for carrying out a methodaccording to the invention comprising a blowing vessel provided withfirst means to coalesce the bubbles rising in the blowing vesselcontents, above each of these being second means for redispersing theair sacs so formed The first means are deflector plates, baffle plates,sieves or the like preferably of funnel-like form which lead to thesecond means for redispersing the air sacs. Advantageously thefunnel-like deflector plates or other first means extend inwards fromthe inside wall of the blowing vessel with the second means forredispersing the air sacs arranged above.

The invention is described in more detail with respect to the drawingwhich shows a longitudinal section of an asphalt blowing vesselaccording to the invention. The waste air line 2 extends from the upperpart of a blowing vessel 1. In the reactor base 3 there is an inputaperture 4 through which a material to be treated that is soft mineraloil distillation residues to be converted into mineral oil asphalt of adesired hardness, can be pumped into the vessel. Branching off from theupper part 1' of the vessel there is also a circulation tube 1" whichdischarges into the vessel near its base 3. The tube 1'' is providedwith a discharge opening 5 through which the finished blowing materialcan be removed. A blowing air line 6 communicates with an airdistributor ring or manifold 7 arranged above the blowing vessel. Goingout from this there are four parallel tubes 8 forming the blowing airline, only three of these being shown in the drawing, with one of thesame being partially broken away for ease of illustration. The tubes 8pass through the upper blowing vessel wall and lead through the vesselto the gas distributor 9, 9' mounted in the region of the base 3 of thevessel. The gas distributor 9, 9' consists of a cylindrical part 9 and adispersing turbine 9. Mouths 8 of the tubes 8 are diverted towards theperipheral surfaces of the part 9. The dispersing turbine 9 is driven bya motor 10, drive shaft 11 of which carries a bevel gear 12 which mesheswith a bevel gear 14 carried by turbine shaft 13. 15 is the lowerposition of the turbine shaft 13. The blowing vessel is filled with theasphalt to be treated up to a level above the point at which thecirculating tube 1" branches off.

Above the gas distributor 9, 9' in the blowing vessel there is a device16 for coalescing the bubbles rising through the asphalt. This device isin the form of a funnel-like deflector plate which extends inwards fromthe wall 17 of the vessel. Instead of the funnel-like deflector plate,other means can be used to coalesce the air bubbles into large air sacs,for example baffle plates or sieves. Above the opening 18 of the bubblecoalescing device formed by the deflector plate there is a device 19 forredispersing the air sacs which have been formed. The device 19 consistsof a redispersing turbine of the same type as the dispersing turbine 9'of the gas distributor 9, 9'. The redispersing device 19 is arrangeddirectly above the bubble fusing device 16. The shaft of theredispersing turbine 9' is an extension 13' of the shaft 13 of thedispersing turbine 9'. Above the redispersing turbine 19 is a furtherbubble coalescing device 16' consisting in the same way as the bubblecoalescing device 16 of a funnel-like deflector plate extending inwardfrom the wall 17 of the reactor, the opening 18' in which leads to afurther redispersing turbine 19 arranged immediately above which isexactly similar to the redispersing turbine 19. This second redispersingturbine 19 is driven by another extension 13" of the shaft 13. 20denotes the upper position ofthe shafts 13, 13', 13".

During the blowing process fresh air is fed to the blowing vesselcontents, that is into the soft asphalt to be converted into mineral oilasphalt of the desired hardness, through the blowing air feed line 6,the air distributor ring or manifold 7 and the tubes 8; the air isdispersed in fine bubbles by the driven gas distributor 9, 9' and thesethen rise through the asphalt. On meeting the deflector plate 16 thebubbles are coalesced into relatively large air sacs which slideobliquely upwards along the funnel-like deflector plate and roll throughthe aperture 18 in the deflector plate to the redispersing device 19 bywhich they are again dispersed into fine bubbles. As has already beenstated, when the bubbles are forcibly coalesced into air sacs the liquidand gaseous phases are extensively separated. The gases forming thebubbles lose contact with the previously surrounding liquid films, whichhave already taken part in the reaction and therefore oppose furtheroxygen diffusion, as these liquid films are so to speak, stripped offthem to be distributed in the asphalt and to go down in this. Theredispersion of the air sacs by the redispersing turbine 19 forms newboundary surfaces between the air and the asphalt at which effectiveoxygen diffusion into the liquid phase can take place so that thematerial is again treated at full intensity. As they rise the newlyformed bubbles again become surrounded by films gradually inhibitingoxygen diflusion which are once again separated from the gaseous phaseby the coalescing device 16, the air sacs thus formed being dispersedinto bubbles by the redispersing turbine 19 above so that new phaseboundary surfaces ready to react are again created. The asphalt in thevessel is continuously circulated using the so-called air-lift pumpingeffect through the circulating tube 1". The waste air collecting abovethe surface of the material is discharged through the pipe 2.

In the following are given the results of comparative tests, the firstpair of tests relating to continuous and the second pair of tests todiscontinuous operation.

a. In a blowing vessel equipped in accordance with the latest prior artand having a fresh air distributor and a redisperser turbine, softasphalt B 200 (softening point as determined by the ring and ball method39 C.; penetration at 25 C., 200 l/ 10 mm.) was continuously blown to amedium asphalt B (softening point as determined by the ring and ballmethod 47 C., penetration at 25 C.; 85 l/lO mm.) at 230 C.

Per ton useful content and blowing day the reactor output was 9.524 kg.B 85 for an air consumption of 86.4 Nm.3 air per ton of convertedproduct.

b. In a blowing vessel as shown in the drawing having a fresh airdistributor and two coalescing and two redispersing devices, the sameinput as in example (a) was continuously blown to the same end productat 230 C.

Per ton useful content and blowing day the reactor output was 15.625 kg.B 85 for an air consumption of 42.24 Nm. per ton of converted product.

c. In a known blowing vessel of the type in example (a) asphalt B 200 ofthe same nature as in example (a) was discontinuously blown to a hardasphalt B 10 (softening point as determined by the ring and ball method:85 C., penetration at 25 C.; 8 H10 mm.) at 230 C.

Per ton useful content and blowing hour the reactor output was kg. B 10for an air consumption of 342.86 Nm. per ton of converted product.

d. In a blowing vessel according to the invention as in example (b) thesame process was carried out as described in (c).

Per ton useful content and blowing hour the reactor output was 250 kg. B10 for an air consumption of only 1 10.0 Nm. per ton of convertedproduct.

c. deflecting said air bubbles to thereby forcibly coalesce the sameinto air sacs; and

d. mechanically agitating said asphalt to thereby forcibly redispersesaid air sacs as air bubbles, whereby fresh air/asphalt phase boundarysurfaces are created.

2. A process according to claim 1, wherein said steps of deflecting saidair bubbles to thereby forcibly coalesce the same into air sacs andmechanically agitating said asphalt to thereby forcibly redisperse saidair sacs as air bubbles are repeated.

2. A process according to claim 1, wherein said steps of deflecting saidair bubbles to thereby forcibly coalesce the same into air sacs andmechanically agitating said asphalt to thereby forcibly redisperse saidair sacs as air bubbles are repeated.